This invention relates generally to the production of kinescopes for color television receivers and particularly to a system and method for measuring the intensity profile of the electron beams of such kinescopes.
The screens of many kinescopes are composed of phosphor stripes each of which emits a different color of light when impacted by electrons. Each kinescope includes an electron gun which provides, electron beams for individually scanning each of the color light emitting phosphors. The electron beams are scanned across the screen in a raster fashion so that each of the electron beams impacts the phosphor which emits the desired light color. The electron beams are individually modulated so that the primary light colors are combined to produce the desired color at each spot on the screen. Because each electron beam must be individually modulated in accordance with the intensity of the beam, it is necessary to measure the intensity profile of the electron beams to permit optimization of the electron beam modulation and other characteristics of the beam.
A current method commonly used in measuring the electron beam profile utilizes a narrow, light transparent slit in an opaque member. The narrow slit is aligned with a photomultiplier tube which measures the light transmission through the slit. The slit is carefully centered over the appropriate color phosphor and the electron beam to be measured slowly scans a raster line across the slit. As the raster line passes the slit, the output voltage of the photomultiplier tube is proportional to the intensity profile of the electron beam. Thus, the intensity profile along one axis, for example, the horizontal axis of the beam is indicated by the change in output of the photomultiplier tube. The slit is then repositioned over a different color producing phosphor line and the process repeated until all the electron beams are measured. The slit is then rotated 90.degree. and the raster lines are swept in a direction 90.degree. to that of the original sweeping and the process repeated to obtain the electron beam intensity profile in the perpendicular, for example vertical, direction.
The above method of measuring the electron beam intensity profile suffers several significant disadvantages. Substantial time and labor are spent mechanically positioning the slit over the phosphor stripes of the various colors. Thus, the measurement of the profiles of all three beams along both the horizontal and vertical axes at one position on the screen necessitates the mechanical positioning of the slit six different times. Typically measurements are taken at various locations on the screen and accordingly the measurements at each location requires the positioning of the slit six times. For this reason, substantially more time is spent in positioning the slit with respect to the phosphor stripes than is spent in actually taking the beam profile measurements. Additionally, because the slit is mechanically positioned with respect to the phosphor stripes, the accuracy of the measurements is dependent upon the positioning of the slit. For these reasons, there is a need for a system and method of electron beam intensity profile measurement which is more accurate and subtantially less time consuming. The present invention fulfills these long felt needs.